Tubular object of polyethylene terephthalate or similar thermoplastic material

ABSTRACT

An object is produced from a tubular blank (10,15,17) of thermoplastic material of polyester or polyamide, preferably of polyethylene terephthalate by reducing the thickness of amorphous material in one or several areas of the blank by means of one or several consecutive re-shaping operations. A mechanical shaping device (23,29,71,81) moves a transitional zone (13,14,113) situated between thicker and thinner material along the blank and simultaneously elongates the blank in the moving direction of the transitional zone while reducing the thickness. After the last re-shaping operation the thinner material preferably has an oriented state. During the re-shaping operation the temperature of the material in the transitional zone (13,14,113) is controlled at a level which, immediately before the re-shaping operation, is within or close to the range of the glass transition temperature (TG). In one embodiment the reduction of the wall thickness of the material is begun in a track (12) in the wall of the blank and continues symmetrically around the track. Clamping devices (41,51,61) are used to maintain the axial position of the blank. The blank is suitable for re-shaping for instance, into a container in which the mouth also consists of oriented material.

This application is a division of application Ser. No. 264,665, filedMay 18, 1981, now U.S. Pat. No. 4,405,546.

FIELD OF THE INVENTION

The present invention relates to a tubular object of polyethyleneterephthalate or similar thermoplastic material obtained from a tubularblank of amorphous material. The object has one or more cylindricalareas of material in which the thickness of the material in the blankhas, in the case of polyethylene terephthalate, been reduced by one ormore shaping operations until it is approximately 1/3 of the originalthickness of the material. In certain applications, the thickness of thematerial is reduced along the entire length of the object. In the areaswith reduced wall thickness the material is axially oriented and has, inthe case of polyethylene terephthalate, a crystallinity of less thanapproximately 30%, usually of the order of 10-25%. The initialtemperature of the material during shaping is preferably below the glasstransition temperature (TG) and the shaping operation takes place withthe temperature of the material controlled in the area of shaping, wherethe material is in surface contact with an external draw ring and/or aninternal shaping device.

PRIOR ART

Previously disclosed in U.S. Pat. No. 4,380,525 is an object in whichthe wall thickness preferably at a central point of said object has beenreduced to approximately 1/3 of the original thickness of the material.The reduction in thickness is produced by clamping each end of a tubularblank in which the material is at an initial temperature below the glasstransition temperature (TG) in two jaws which are then moved apart. Bycausing an annular area of the material to have a higher temperaturethan the surrounding material, the obtained material properties of thearea will cause the reduction in thickness to commence in the areaduring the stretching operation. In certain applications, the internaldiameter of the blank is stabilized by the use of an internal mandrel.The process as disclosed will produce an object in which the material isaxially oriented and has a crystallinity of less than approximately 30%,usually being of the order of 10-25%.

Already disclosed in U.S. Pat. No. 4,374,878 is a method for causing thethickness of the material in a tubular blank to be reduced mechanicallyby the use of an external device. The device consists of one or morerollers which make contact with the external and/or internal surface ofthe blank with such force that the desired reduction in thickness willoccur as the initial temperature of the material approaches the glasstransition temperature. The external device is moved around theperiphery of the blank and along the axis of the blank simultaneously.This method will also produce an object in which the crystallinity inthe areas of reduced material thickness will be less than approximately30% and will be of the order of 10-25%.

However, the material will not have been oriented axially to such a highdegree as when the process described in the previous paragraph is used.

In accordance with the inventions described above, certain applicationswill produce objects which differ in respect of the transitional zonebetween stretched and non-stretched material. This condition will arise,for instance, if a central section of a tubular blank is stretched whilethe material in the blank is at an initial temperature below the glasstransition temperature (TG) and if the blank is then separated into twoparts so as to form two separate objects. The difference is due to thefact that one of the objects contains the start zone for the yielding ofmaterial produced by the stretching operation, while the other objectcontains the stop zone for the yielding of material.

When practising the invention in accordance with U.S. Pat. No. 4,380,525an annular transitional zone between the thinner material which has beenstretched and the thicker material which has not been stretched willnormally be produced. In the zone the surface of the material will forman angle of approximately 45° with the surfaces of the stretched andnon-stretched material respectively. Axially displaced tapering areaswill occasionally be produced in the essentially annular transitionalzone during the drawing operation, the presence of said areas usuallyrequiring the object to be scrapped.

SUMMARY OF THE INVENTION

The present invention contemplates apparatus tubular objects with areasof the wall in which, in the case of polyethylene terephthalate, theoriginal thickness has been reduced to approximately 1/3 of its initialvalue, in which areas the material is oriented mainly along the axis ofthe object only, in which areas crystallinity is less than approximately30% and is preferably within the range of 10-25%, and in which areas thecrystallinity produced in the material by the aforementioned orientationwill achieve a maximum value of 17%. The material in these areas willalso have been oriented mainly along the axis of the object.

The speed at which the thickness of the material is reduced is greaterin accordance with the present invention than by previously disclosedmethods. Furthermore, the transitional zone between material with theoriginal wall thickness and material with reduced wall thickness willalways have a predetermined shape, at the same time as the length of thesections with reduced wall thickness will always be precisely defineddue to the fact that the re-shaping of the blank in the transitionalzone itself is mechanically controlled. For example, when starting froma tubular blank in order to make an object to be used for two preformswhich face each other, the rate of production will additionally bedoubled by starting the drawing operation at a central point and by thencontinuing it simultaneously towards the two ends of the tube. Theobject which has thus been produced may be cut and the cut sectionssealed to form two preforms for future processing, in which thetransitional zone between material with the original wall thickness andmaterial with reduced wall thickness will always have a predeterminedshape and will always contain material with characteristics which areidential from one preform to another.

In accordance with the present invention, it is also possible to producean object in which the thickness of the material is reduced along theentire length of the object or in one or more cylindrical sections ofthe object. The object is in the form of a tube which is open at bothends or, in certain applications, in the form of a tube which has beensealed at one end. The object is mainly intended to be moulded intocontainers, whereby each single object is formed into either a singlecontainer or a number of containers. In the latter case, the object isdivided into a number of parts which are then moulded into containers.

The production of an object of polyethylene terephthalate in accordancewith the present invention starts with a tubular blank or a similarthermoplastic material. The material in this blank will be in anamorphous state. In one single operation or a number of consecutiveoperations the thickness of the material in the blank is reduced toapproximately 1/3 of its original thickness. This reduction in thicknesstakes place either along the entire length of the blank or in one ormore sections of the blank. Use is made of a draw ring in certainapplications, in which the relationship between the internalcircumference of the draw ring and the external circumference of theblank is such that the thickness of the material will be reduced as thedraw ring is moved axially along the blank. The temperature of thematerial immediately before the reduction in thickness takes place mustbe in the range of or lower than the glass transition temperature whichwill be abbreviated as TG hereafter, and should deviate from TGpreferably by no more than 15° C. Although the technical effect of thepresent invention may be achieved at a much lower temperature, it isadvantageous to use an initial temperature close to TG, for instance atemperature which is between 1° to 3° C. below TG, since material atthis initial temperature will permit the draw ring to be moved at highspeed. In certain typical applications, the draw ring operates inconjunction with an internal shaping device located inside the blank,whereby the external dimension of the shaping device fits the internalsurface of the blank. In other applications only the internal shapingdevice is used. The thickness of the material in the blank is reduced bycontact with the draw ring and/or the internal shaping device as saiddraw ring and/or shaping device is moved axially along the blank. Duringthe re-shaping operation a transitional zone is formed between materialwith the original thickness and material with reduced thickness, saidtransitional zone gradually moving axially along the blank. The materialin the transitional zone is kept at a temperature close to TG during there-shaping operation by the transfer of heat to the draw ring and/or theshaping device located inside the tubular blank. In certain applicationsthe material in the transitional zone is, however, allowed to assume atemperature which exceeds TG by no more than 30° C., and preferably byno more than 15° C.

In certain applications the material in the area adjacent to thetransitional zone is cooled to a temperature below TG immediately afterit has been reduced in thickness.

In accordance with the present invention, the possibility is offered ofproducing an object with areas with mainly monoaxial orientation and inwhich the material has been reduced in thickness and whose externalcircumference has been reduced and/or the internal circumference hasbeen increased compared to the circumference of the correspondingsections of material in the blank.

In the case of sections with reduced wall thickness requiring to beproduced in areas situated between the ends of the blank, the reductionin thickness is begun by forming one or more peripheral grooves in thewall of the blank at the same time as external devices are used tosubject the blank to tensile stress along its axis. This stretchingoperation reduces the wall thickness in the grooves to about 1/3 of itsoriginal thickness at the same time that the blank is elongated axially.Further reduction of the thickness of the wall of the blank is producedby positioning the draw ring in the aforementioned groove or grooves andmoving it axially along the blank. Certain applications use two rings,whereby the reduction in wall thickness takes place simultaneously froma specific groove outwards towards the two ends of the blank.

In the case of a blank which is sealed at one end and in which the wallthickness is to be reduced adjacent to the seal, the draw ring shouldpreferably be moved from the seal towards the other end of the blank. Incertain applications the reduction in thickness is allowed to continuealong the entire length of the blank.

In those applications in which the blank is in the form of a tube openat both ends, this may be sealed in certain cases after the reduction inthickness by heating the material at one end of the object and then bypress moulding the material in a mould which may be cup-shaped, forinstance. German Patent DE PS No. 1 704 119 contains examples of methodssuitable for achieving sealing of this kind.

The reduction of the thickness of the material in several stages is usedmainly in the event that the material is so thick that problems arise intransferring sufficient heat away from the transitional zone. Byreducing the thickness of the material a number of times before thefinal reduction in thickness is made, a thinner material will beproduced which will facilitate the transfer of heat away from thetransitional zone to the adjacent draw ring and/or internal shapingdevice.

Two draw rings are included in one device for producing an object inaccordance with the invention. A mandrel around which a tubular blank isplaced during the drawing operation is positioned axially inside the twodraw rings. Separate clamping devices are also positioned near the endsections of the blank. Each draw ring consists of two draw ring halveswhich are moved by the driving device between an operating position inwhich the halves of the draw ring are in contact with each other and anopen position in which the halves of the draw ring are separated fromeach other. The open position is used when inserting the tubular blankor removing the made object from the device.

Driving devices are also positioned in such a way as to move the drawrings and clamping devices axially along the blank. At least while thedraw rings are moving towards the ends of the tubular blank, themovement of the draw rings is connected to the movement of the clampingdevices in such a way that the draw ring and clamping device which areadjacent to each other are moved in the same direction and in such a waythat the correlation between the speed of the respective draw ring andclamping device is determined by the reduction in thickness which it iswished to produce in the material in the tubular blank. For example,when reducing the wall thickness of the blank to 1/3 of its originalthickness, the ratio between the speeds of the clamping device and thedraw ring shall be 2/3, with a ratio of 1/2 when reducing the thicknessof the material to 1/2 of its original thickness, etc.

The clamping devices are fitted with axially movable spring componentsagainst which the edges of the tubular blank make contact. Anylongtitudinal tolerances which are present in the blank both before andduring the drawing operation are absorbed by the spring components.

In one embodiment of the invention, each draw ring usually consists ofthree ring sections with a certain degree of thermal insulation betweenthe sections. Each ring section is provided with channels for a fluid,said fluid either heating or cooling the ring section. Theaforementioned mandrel is also provided with liquid channels. Thecentral ring section includes that part of the draw ring against whichthe transitional zone between material with its original thickness andmaterial with reduced wall thickness is formed during the drawing of thetubular blank. Of the neighbouring ring sections, the one with thelargest internal diameter is in contact with the material with itsoriginal thickness during the drawing operation, while the other ringsection with the smallest internal diameter is in contact with thematerial with reduced thickness.

When drawing a tubular blank, said blank is positioned on the mandrel insuch a way that it is held securely by the clamping devices. A centralperipheral groove in the base of which the wall thickness has beenreduced to approximately 1/3 of its original thickness is formed in thetubular blank in the manner described above. The draw ring halves arethen moved to their operating position. The shape and the axial lengthof those parts of the draw rings which are introduced into the groovematch the shape and the axial length of the groove. The material of theblank in the area which is to be drawn should preferably be heated to atemperature close to but below TG before the blank is positioned on themandrel. The material will be raised to the correct drawing temperaturethrough the contact surfaces formed between the material of the blankand the draw rings and mandrel.

During the actual drawing operation, the draw rings and the clampingdevices are moved away from the groove by the driving devices, while theaforementioned relative speed between the draw rings and the clampingdevices is maintained. Thus the thickness of the material in the blankwill continue to be reduced by the draw rings for as long as movementcontinues. At the same time the blank is lengthened along its axis.

An essential factor relating to the device is the control of thetemperature of the material in the transitional zone between amorphousmaterial with the original wall thickness and material which has beenreduced in thickness. The draw ring has an internal profile whichmatches the change in the thickness of the material which occurs in thetransitional zone. The profile has been selected in such a way that itwill form contact surfaces with the internal surface of the draw ringnot only in the transitional zone, but also ahead of and after it duringthe drawing operation. The draw ring is able, in this way to control theshape of the transitional surface in the transitional zone. Thetemperature of the material in the blank is regulated during the entiredrawing operation by the transfer of heat between the material in theblank and the draw rings and/or the mandrel. It is particularlyimportant that the section of the draw ring which is in contact with thematerial in the transitional zone should maintain the material in theblank at a temperature close to TG.

A simplified embodiment of the present invention makes use of a singledraw ring which is moved from a starting groove preferably all the wayto the edge at one of the ends of the blank. In this way an object isproduced in which the wall thickness is reduced at one end only. Thisembodiment preferably makes use of an internal mandrel as a dolly whichwill take up the axial forces which arise as the wall thickness isreduced. The movement of the draw ring is interrupted in certainapplications before it passes over the edge of the tubular blank. Theedge will thus be bordered by rim in which the wall thickness has notbeen reduced after the drawing operation is complete. The object whichis produced in this way is suitable for use as a preform, possibly aftera certain amount of re-shaping of the rim, i.e. which will become theedge of the mouth, for a container intended to be closed by means of a"crown cork", for instance. Before the object is moulded into acontainer, the area which will become the mouth is stabilized by heatingand by thermal crystallization, with crystallization usually beingallowed to continue until the material in the aforementioned rim becomesopaque.

In a preferred embodiment of the present invention the blank is providedwith a starting track or groove of such axial length that space isprovided in the track for a clamping device together with the draw ringor draw rings. At least during the initial stage of the movement of thedraw ring or draw rings, the clamping device holds sections of the wallof the material in the base of the track pressed against the mandrel. Inthis way the position of the blank relative to the mandrel is fixed. Inthe embodiment of the present invention in which two draw rings aremoved away from each other, the clamping device is designed to hold thewall of the blank in an area situated between the draw rings. By holdingthe blank securely against the mandrel, this will prevent any axialmovement of the blank in relation to the mandrel which might arisedepending on the axial forces which occur at the contact surfacesbetween the respective draw ring and the material in the transitionalzone between the wall of the blank with reduced thickness and the wallof the blank with non-reduced thickness. Any movement could, forinstance, lead to the disadvantage that in the variant of the inventionin which an area surrounding the track has the thickness of its wallreduced, the area with reduced wall thickness may be positionedunsymmetrically in relation to the starting track.

The use of a clamping device in accordance with the previous paragraphoffers the possibility of producing any desired axial length in the areain which the wall thickness of the material has been reduced. In certainapplications this involves producing such a reduction in the thicknessof the wall of the material along the entire length of the blank,whereas in other applications the reduction in thickness is interruptedbefore the draw ring or draw rings reach and pass beyond the end or endsof the blank. By leaving an area of amorphous material at the very endor ends of the blank, a section of material will be produced which ishighly suitable, for example, for sealing to produce the base of apreform by the use of a method which is described in German Patent DE PSNo. 1 704 119 or, after having been subjected to thermalcrystallization, for forming a rim for use with the "crown cork" type ofclosure.

In an alternative embodiment, the draw ring is used to reduce the wallthickness of the material in a tubular blank with a sealed bottom, themouth of which is already provided with a means of closure, for examplescrew threads. The blank in which the material is intended to besubjected to a reduction in thickness is produced by a conventionalmethod, for example by injection moulding or by extrusion followed bysealing and moulding the bottom and mouth. In certain applications, thestarting track is formed in the manner described above, while in otherapplications a starting point or the starting track in whole or partlyis produced during the injection moulding of the preform.

When using an external draw ring to reduce the thickness of the materialin the wall of the blank, a certain reduction in the internal diameterof the blank will also be produced, as has already been mentioned. Themandrel inside the blank thus acts as a shaping device which willdetermine the extent of the reduction in diameter. Surprisingly, it hasbeen found that, for material within the range of temperatures indicatedabove during the re-shaping operation, the contact between the wall ofthe material and the mandrel and produced by the contraction, generatesrelatively little contact pressure between the internal surface of thewall of the blank and the external surface of the mandrel, for whichreason no problems are encountered in removing the finished blank fromthe mandrel after the shaping (drawing) of the blank is complete.

No internal mandrel is called for in certain types of application forthe device, in which the object is allowed to assume an internalcircumference which is smaller than its original circumference. Byselecting an internal mandrel with an external circumference which issmaller than the internal circumference of the blank, it is possible inother typical applications to control the reduction in the internalcircumference of the blank during the drawing operation to a value whichis suitable for the envisaged specific application.

BRIEF DESCRIPTION OF THE FIGURES OF THE DRAWING

The present invention is described in greater detail with reference to anumber of figures, in which

FIG. 1 shows a perspective view of a drawing device;

FIG. 2 shows a longitudinal section through the drawing device in FIG. 1in which the draw rings of the drawing device are in the initialposition before drawing;

FIG. 3 shows part of a longitudinal section corresponding to FIG. 2, inwhich the draw rings have been separated from each other;

FIG. 4 shows a support plate fitted with a draw ring in its operatingposition;

FIG. 5 shows a longitudinal section through a tubular blank with a drawring in its initial position;

FIG. 6 shows a longitudinal section through a tubular blank duringdrawing in the direction away from its sealed part;

FIG. 7 shows a section through a tubular blank with a draw ring in theinitial position prior to drawing the blank in a short section at oneend;

FIG. 8 shows a section of the tubular blank in FIG. 7 with the draw ringin its final position;

FIG. 9 shows a longitudinal section through a drawing device with acentral clamping device and with the draw rings or the clamping devicein the initial position before drawing;

FIG. 10 shows part of a longitudinal section corresponding to FIG. 9with the draw rings moved apart;

FIG. 11 shows the central area in accordance with FIG. 9 in detail;

FIG. 12 shows the central area in accordance with FIG. 10 in detail;

FIGS. 13, 14 and 15 show alternative embodiments.

DETAILED DESCRIPTION

FIG. 1, which shows an overall perspective view of a drawing device inaccordance with the present invention, includes a base 30 from which anumber of guide pins 31a-31d project vertically. The rest of thedescription which follows will relate to the device in this position,although the concept of the invention is in no way restricted to aspecial position of this kind. The designations "upper" or "lower" orother similar designations are occasionally used below in connectionwith a variety of components, said designations being used only for thepurpose of clarification.

The base is fitted with driving devices with gearing (not shown in thefigure) for a number of drive screws 32a-32d which lie parallel with theguide pins. Four support plates 50,60,70,80 are positioned at rightangles to the guide pins and the drive screws. Each support plate isfitted with bearings which fit the guide pins 31a-31d and threaded holes52a-52d,62a-62d,72a-72d,82a-82d which operate in conjunction with anumber of the drive screws 32a-32d. The plates are also provided withopenings 58a-d,68a-d,78a-d,88a-d for those drive screws which are not inthreaded contact with the actual support plate. The top and bottomsupport plates 50 and 60 are arranged to operate in conjunction with thetwo drive screws 32a and c, whereas the two interjacent support plates70 and 80 are arranged to operate in conjunction with the two remainingdrive screws 32b and d. Furthermore, the upper parts of the drive screwswhich operate in conjunction with the support plates 50 and 70 arethreaded in opposite directions to the lower parts of the drive screwswhich operate in conjunction with the support plates 60 and 80. Thismeans that as the drive screws are rotated the two upper support plateswill move in the same direction, although this will be opposite thedirection in which the two lower support plates move.

Since the top and bottom support plates are driven by the screws 32a andc and the two middle support plates are driven by the screws 32b and d,the speed at which the respective support plates move will be determinedby the rotational speed and the pitch of the screws in conjunction withwhich the respective support plates operate. The pitch of the thread onthe drive screws is selected in such a way that the top and bottomsupport plates will always move at a lower speed than the two plates inthe middle. In the initial position, the two middle plates will be inclose contact with each other and the top and bottom plates will be inpositions which will allow movement to take place towards the ends ofthe guide pins. After movement has taken place, the middle supportplates will have moved closer to the upper and lower support platerespectively.

The top support plate 50 and the bottom support plate 60 are providedwith clamping devices 51 and 61, each of which holds one end of atubular blank 10. The blank is provided with a preferably centralperipheral starting track or groove 12 (FIG. 2) in which the thicknessof the material is approximately 1/3 of its original thickness. Thestarting track is formed preferably before the blank is positioned inthe device by the application of external pressure to the wall of thematerial, for instance by means of a number of interacting rollers, atthe same time that the tubular blank is subjected to tensile stressesalong its axis. When forming the starting track, the use of rollers inconjunction with the stretching operation produces a track with apredetermined axial length which is thus given a profile which issubstantially identical with the profile of those parts of the drawrings which are introduced into the track (see description of FIG. 2below) when re-shaping the blank into the object. The tubular blank iscaused to lengthen axially when the starting track is formed.

The two middle support plates 70 and 80 are each fitted with a draw ring71 and 81, with the latter draw ring being obscured in FIG. 1. Theclamping device 51 of the top support plate and the draw rings 71,81 ofthe two middle support plates respectively consist of two halves 51a,b,71a,b and 81a,b which are moved by the driving devices53a,53b,73a,73b,83a and 83b to and from the closed position shown inFIG. 1.

In FIG. 2, which shows a longtitudinal section through the drawingdevice in accordance with FIG. 1, the left-hand part of the figureportrays the device with the upper clamping device 51 and the two drawrings 71,81 in their open position, and the right-hand part of thefigure portrays the device with the upper clamping device 51 and the twodraw rings 71,81 in their closed position (operating position).

The figure also shows the blank 10. At its center is the peripheralstarting track 12 which is formed in accordance with the abovedescription.

In additional to the details shown in FIG. 1, FIG. 2 shows that theupper and lower clamping devices 51,61 are respectively fitted withsprung support plates 54a,54b and 64 against which the end edges of thetubular blank 10 make contact. The required spring function is providedby springs 55a,55b and 65a,65b around guiding devices 56a,56b and66a-66b for the support plates 54a,54b and 64, with the guiding devicesscrewed firmly to the support plates.

FIG. 2 also shows that the two draw rings 71 and 81 consist of two drawring halves 71a,b and 81a,b. Each draw ring is divided into threesections 74a,b,75a,b,76a,b84a,b,85a,b,86a,b, each of which consists inturn of two ring section halves. The ring sections are separated fromeach other by a certain degree of thermal insulation. The ring sectionsare held together by means of ring casings 77a,b and 87a,b in such a waythat they will combine to form the two halves of the draw rings. Eachring section is provided with channels 174a,b,175a,b,176a,b and184a,b,185a,b,186a,b to permit the flow of liquid.

The draw ring sections are in the form of sections 74a,b and 84a,b withan internal circumference which matches the circumference of thematerial in the blank in the areas in which the thickness of thematerial has not been reduced, further sections 76 and 86 with aninternal circumference which matches the circumference of the materialin the blank in the areas in which the thickness of the material hasbeen reduced, and further sections 75a,b and 85a,b which form contactsurfaces with the material in the transitional zone between material inthe blank which has and which has not been reduced in thickness.

Finally, FIG. 2 shows a mandrel 20 which is fitted in the internalsurface of the blank 10 and which is provided with liquid channels 21.

FIG. 3 shows part of a longtitudinal section which corresponds tocentral sections of FIG. 2 in which the draw rings have moved or are inthe course of moving apart along the axis of the blank, and portrays acentral section 11 of a blank in which the thickness of the material inthe blank 10' has been reduced. At the transitional zone 13,14 betweenmaterial with its original wall thickness and material with reduced wallthickness, contact surfaces are formed between the middle draw rings75a,b,85a,b and the material in the transitional zone. In this way thedraw rings are able to control the shape of the transitional surfacebetween material with its original wall thickness and material withreduced wall thickness.

FIG. 4 shows the support plate 70 viewed from above and with the drawring 71 in its closed position. The figure also illustrates thelocations of the bearings for the guide pins 31a-d and the openings78b,d and for the threaded holes 72a,b for the drive screws 32b,d. Theother support plates which are fitted with the draw ring 81 or with theclamping devices 51 or 61 are similarly equipped. As has already beenmentioned, the clamping device 61 is not divided, and has thereforenothing corresponding to he driving device 73a,b.

FIGS. 5 and 6 show a typical application of the present invention inwhich the wall thickness of a tubular blank 15,15' which is sealed atone end is reduced, starting at the sealed end of the blank. Thisrequires a draw ring 23 to be dimensioned preferably in such a way thatboth before and at the start of the drawing operation contact will bemade between the middle ring section and the upper ring section and theouter surface of the tubular blank. Here too the draw ring is made up ofthree ring sections 24,25,26 with liquid channels 124,125,126. The ringsections are dimensioned in a similar fashion to the ring sections whichhave already been described and are held together by a ring casing 27. Amandrel 28 operates in conjunction with the draw ring 23 in there-shaping of the blank. The mandrel is normally provided with liquidchannels, which is not illustated in FIGS. 5 and 6, however.

FIG. 6 shows the manner in which re-shaping is begun and in which asection 16 of the blank with reduced wall thickness is formed in thelower section of the blank. Re-shaping normally continues until all thematerial in the cylindrical part of the blank has had its wall thicknessreduced. In the event that the mouth has already been formed, which maybe the case with an injection-moulded blank, the re-shaping of the blankis, of course, interrupted as the draw ring reaches the mouth. Thetransitional zone between material with its original wall thickness andmaterial with reduced wall thickness is indicated in FIG. 6 by numeral113.

FIGS. 7 and 8 show an alternative embodiment of the present invention inwhich a draw ring 29 is composed of only two ring sections 96a,b,97a,bwith separate liquid channels 94a,b,95a,b. In this application too thereshould preferably be a certain degree of thermal insulation between thering sections. If necessary, the draw ring may be extended by theaddition of a third ring section with a separate liquid channel andwhich is dimensioned in the manner already described. Here too the drawring operates in conjunction with an internal mandrel 28, which isnormally provided with liquid channels but not shown in the figures. Thedraw ring re-shapes the mouth of a tubular blank 17 which is sealed atone end. In an area which is usually quite close to the opening in theblank, there will be a peripheral starting track 19 in which thethickness of the material has been reduced to approximately 1/3 of itsoriginal thickness. The starting track is produced in the manner whichhas already been described.

In FIG. 8 the draw ring 29 has been moved relative to the blank with thehelp of the mandrel 28 in such a way that a section 18 of the blank withreduced wall thickness is produced adjacent to the opening in the blank17'.

FIGS. 9 and 10 show a further alternative embodiment of the presentinvention in which a central clamping device 41a,b is located in thearea between the draw rings 71 and 81. The clamping device is positionedon a central support plate 40a,b with a fixed position in the device.This fixed position is obtained, for example by attaching the supportplate to the guide pins 31a,b. The central support plate is also fittedwith driving devices 43a,b for moving the two parts 41a,b of the centralclamping device to and from the operating position of the respectiveparts. In certain embodiments, the central clamping device is providedwith liquid channels 141a,b. Other devices shown in FIGS. 9 and 10correspond to devices shown in FIGS. 1-4, in which case their referencenumbers agree with the reference numbers in those figures. An equivalentdevice to the clamping device 51 is not present in this embodiment.

FIGS. 11 and 12 show details of the central areas in FIGS. 9 and 10,i.e. those areas in which the wall of the material in the blank isprovided with a starting track or in which the wall of the material hasundergone a reduction in thickness in conjunction with the movement ofthe draw rings. The reference characture 112 is used to indicate an areaof contact between the internal surface of the blank 10,10' and theexternal surface of the mandrel 20 caused by a certain amount ofdeformation in the wall of the blank produced by the clamping device 41awhen this is in the operating position. The reference characters 115,116indicate areas of contact with the mandrel by the internal surface ofsections of the material in the blank 10' whose thickness has beenreduced by the drawing operation.

In accordance with the present invention, the central clamping device41a,b may be designed in accordance with several alternativeembodiments. These are characterized by the fact that the clampingdevice 41a,b in its operating position surrounds the wall of the blank,thus forming contact surfaces with the external surface of the wall ofthe blank which are distributed at various points around the peripheryof the blank. This distribution of the contact surfaces is produced bythe clamping device for example by the surfaces of the clamping devicewhich face the blank not being in the form of cylindrical surfaces ofcircular cross-section, but rather in the form of cylindrical surfacesof, for instance, elliptical or polygonal cross-section.

FIGS. 13-15 show examples of objects 210', 210", 210'" in accordancewith the invention. The object 210' in FIG. 13 has at its lower part acylindrical wall section 213 of amorphous material adjacent to a sealedbottom 211' also of amorphous material. FIG. 14 shows object 210" inwhich the external cylindrical surface has the same diameter along theentire length of the object. The sealed bottom 211" of the object isalso of amorphous material in this embodiment. Finally, FIG. 15 shows anembodiment in which the edge of the mouth 212 of the object consists ofmaterial with its original thickness, whereas the remaining parts of theobject are similar in design to those in FIG. 14.

The blank 10 is positioned over the mandrel 20 in the embodiment of thepresent invention in accordance with the typical example shown in FIGS.1-4. The clamping device 51 and the draw rings 71 and 81 will then be intheir open position, corresponding to the position shown in theleft-hand part of FIG. 2. The blank which is placed around the mandrelforms the contact surfaces with the mandrel. Once the blank is in placeand is in contact with the sprung support plate 64 of the lower clampingdevice 61 the upper clamping device 51 and the draw ring halves are thenmoved to their closed position. The two draw rings 71 and 81 enter thestarting track 12 and in so doing form contact surfaces with the outerwall of the blank where the wall thickness has not been reduced, wherethe wall thickness has been reduced to its minimum value, and at thetransitional zone between the two aforementioned areas.

The material of the blank will preferably be at a high temperature,although preferably below TG, when it is placed on the mandrel. Thefinal temperature of the material is set by the transfer of heat betweenthe mandrel and the blank and/or between the draw rings and the blank.The temperature is controlled by means of the liquid which flows throughthe liquid channels 21 in the mandrel and/or through the liquid channels174a,b,175a,b,176a,b and 184a,b,185a,b,186a,b in the draw rings. Thethermal insulation which is present between the ring sections of thedraw rings generally maintains a certain difference in temperaturebetween different areas of material in the blank. The ring sections74a,b,84a,b with the largest internal diameter will, when in theposition shown in the right-hand part of FIG. 2, set the material to atemperature in the range of or just below TG, and preferably to atemperature which is not more than 15° C. below TG. The ring sections75a,b,85a,b have a similar function, whereas the ring sections 76,86preferably will maintain a temperature well below TG, and preferably ata temperature which is at least 15° C. below TG, in order to cool thematerial once it has undergone the reduction in thickness.

Once the material has reached the specified temperatures the drivingdevices at the base will begin to rotate the driving screws 32a-d,causing the support plates 50,70 and the associated clamping device 51and draw ring 71 to move upwards in the figures, and the support plates60,80 and the associated clamping device 61 and draw ring 81 to movedownwards in the figures. The thickness of the material in the blank isthus reduced by the draw rings as long as movement continues. At thesame time, the blank will be lengthened axially and this elongation willbe proportional to the reduction in the thickness of the material and tothe axial movement of the draw rings. The speeds at which the supportplates 50 and 60 move are therefore selected in such a way that thepositions of the clamping devices 51,61 will match the elongation of theblank. Any irregularities which may occur will be absorbed by thebiassed support plates 54 and 64.

The middle draw rings 75a,b and 85a,b are in contact with thetransitional zone between material with reduced thickness and materialwith its original thickness. The profile of the middle ring section isselected in such a way that the material during the re-shaping operationwill form contact surfaces with the internal surfaces of the ringsection. In this way the ring section will control the shape of thetransitional surface between material with reduced thickness andmaterial with its original thickness. The ring section also has atemperature regulating function in that the transfer of heat takes placeat the aforementioned contact surfaces in such a way that the materialin the transitional zone is maintained at a temperature close to TGthroughout the entire drawing operation. It is essential, particularlywhen drawing takes place at high speed or when the material used is verythick, that the middle draw ring should have excellent heat conductingproperties so that the material in the transitional zone will not reachtoo high a temperature.

Once the draw rings have been moved apart so that the central section 11of the blank will be given a predetermined length, the movement of thesupport plates is stopped. The driving devices 53a,b,73a,b,83a,b thenmove the clamping device 51 and the draw rings 71 and 81 to their openposition, and the object which has been formed in the manner describedis then removed from the mandrel, whereupon a new tubular blank isplaced on the mandrel and the operation is repeated.

The section 11 with reduced wall thickness in the finished object formsthe central section at which the object is cut in order to produce twosymmetrical parts. Each part is then sealed at the end with its originalwall thickness, thus producing a preform which may be used, for example,to produce a blow-moulded container. Those sections of the preform whichhave reduced wall thickness are subsequently re-shaped to form the basisfor the mouth of the future container.

In the application of the embodiment of the present invention shown inFIGS. 5 and 6, the function is in principle identical with thatdescribed above. The internal mandrel 28 acts as a dolly which takes upthose forces which arise as the draw ring 23 is moved axially along theblank. Regulation of the temperature in the different areas of thematerial is also important in this typical application. The mandrel 28is normally provided with liquid channels corresponding to the liquidchannels 21 in the mandrel 20 shown in FIGS. 2 and 3. In certain typicalapplications the thickness of all the material in the cylindricalsection of the blank is reduced, while the re-shaping stops sooner inother typical applications.

The embodiment shown in FIGS. 7 and 8 is applicable in those cases inwhich it is required to produce a number of areas of material in whichthe thickness of the material has been reduced. Each such area ofmaterial requires a starting track in which the reduction in thethickness of the material may begin. When producing the object the drawring 29 is moved to an initial starting track and the halves of the drawring take up their operating position. The draw ring is moved from thestarting track over a short distance along the axis of the blank,reducing the thickness of the material until the first section ofmaterial with reduced wall thickness has been produced. The draw ringhalves are then moved apart and the draw ring is moved to the nextstarting track, when the draw ring halves take up their new operatingposition. The draw ring is now moved once more along the axis of theblank in order to produce a new area of material with reduced wallthickness, and so on. The operation is repeated until the desired numberof areas with reduced material thickness have been produced.

The blank used in conjunction with the unidirectional drawing describedin connection with FIGS. 5-8 is shown as being sealed at one end. Inthis way the seal will have operated in conjunction with an internalmandrel to absorb the axial forces required during the drawingoperation. It is, of course, possible to use external clamping deviceswhich replace the function of the mandrel in this respect. Thisalternative is used when drawing tubular blanks which are open at bothends.

In the application of the present invention which utilizes theembodiment shown in FIGS. 9-12, the blank 10 is slid over the mandrel 20until it makes contact with the lower clamping device 61. In this casethe latter serves as a means for determining the axial position of theblank, thereby ensuring that the track 12 on the blank adopts a positionwhich is suitable for the positioning of the draw rings 71,81 and forthe clamping device 41a,b. This situation corresponds to the left-handhalf of FIG. 9. The driving devices 43a,b,73a,b,83a,b then move theclamping device 41a,b and the draw rings 71,81 into contact with theexternal surface of the blank in and adjacent to the track 12. Thetemperature conditioning of the material in the blank then takes placein the manner which has already been described, in addition to which incertain typical applications liquid is also caused to flow through thechannels 141a,b in the clamping device 41a,b. This situation correspondsto what is shown in the right-hand part of FIG. 9 and in detail in FIG.11.

In its operating position, the central clamping device 41a,b surroundsthe blank 10 in the bottom of the track 12. This forms contact surfaceswith the bottom of the track which are divided into a number of areasaround the circumference of the blank. The contact pressure present atthese surfaces in turn causes the internal surface of the blank and thesurface of the mandrel to bear against each other. The bearing surfacesadopt positions which correspond to the distribution of the contactsurfaces. The bearing surfaces are produced because the clamping devicedeforms the shape of the surface defining the internal limits of theblank. The contact pressure of the clamping device is selected in such away that in the event that the shape is deformed, the thickness of thematerial in the bottom of the track will remain largely unchanged. Abearing surface is shown in detail in FIG. 12 and is designated by thereference character 112.

The driving devices in the base 30 (FIG. 1) then rotate the drivingscrews 32a-d causing the draw rings 71,81 to move apart along the axisof the blank, simultaneously re-shaping the wall of the material andelongating the blank. The friction between the blank and the mandrel atthe aforementioned bearing surfaces 112 fixes the position of the blankon the mandrel and ensures that the re-shaping of the blank will takeplace symmetrically around the track 12. The driving of the supportplate 60 is selected in such a way that the clamping device 61 will beaway reliably from the end of the tube so as not to have any effect onthe elongation of the tube which occurs in conjunction with thereduction in the thickness of the wall of the blank. This operatingsituation corresponds to FIGS. 10 and 12. FIG. 12 also shows that, inaddition to the stretching of the material which occurs during there-shaping of the wall of the blank, contraction of the blank also takesplace, causing its internal surface to be moved into contact with themandrel 20. These contact surfaces are indicated in the figure by thereference characters 115,116. The formation of these contact surfacescontributes to the fixing of the position of the blank relative to themandrel which is achieved with the help of the central clamping device41a,b. It has been found in the majority of typical applications thatadditional fixing by means of the contact surfaces 115,116 is notessential to achieving the desired symmetrical re-shaping of the blank.

The description in the previous paragraph indicates that the alternativeembodiment of the invention in accordance with FIGS. 9-12 will permitany desired length of the blank to have the thickness of its materialreduced. It is thus possible to reduce the thickness of the materialalong the entire length of the blank, to interrupt the reduction inthickness immediately before the ends of the blank, or else to reducethe thickness in a number of areas distributed axially along the blankand separated by sections of material in which there has been noreduction in thickness. In each area with reduced material thickness,the reduction of the thickness is begun in a new starting track.

Surprisingly, it has been found that when the blank is re-shaped at thetemperatures indicated above, relatively low contact pressure isproduced between the material of the blank and the mandrel, for whichreason no problems are encountered in removing the moulded object fromthe mandrel after the moulding operation is completed.

The objects shown in FIGS. 13-15 are examples of objects produced inaccordance with the above description. When producing an object inaccordance with FIG. 13 the thickness is reduced in one preferredembodiment in a tubular blank which is open at both ends, whereby at theend of the blank which will subsequently be sealed an area of amorphousmaterial is left which is then heated and sealed in accordance with themethod described above. Figures 14 and 15 relate to embodiments in whichan already sealed tubular blank of amorphous material is givencylindrical areas of the walls consisting of essentially monoaxiallyoriented material. In FIG. 14 the monoaxially oriented material ispresent around the object over its entire length, whereas in FIG. 15 theedge of the mouth 212 consists of material which has not undergone suchorientation.

The concept of the invention also contains the possibility of furtherincreasing the crystallinity by heating the material, over and above thecrystallinity which is produced in the material in conjunction with themonoaxial orientation. This crystallinity should not be allowed tocontinue to such a point that the ability of the material to undergofurther re-shaping is impaired in the case of an object which is apreform which will be re-shaped in a subsequent operation to produce afinished article. The crystallinity of an object is normally allowed toreach a maximum level of approximately 30% when the object is to undergofurther re-shaping. Crystallinity is preferably allowed to lie between10-25%, whereas the crystallinity produced by monoaxial orientation willachieve a maximum value of approximately 17%.

It has been assumed in the above description that the reduction in thethickness of the material until it reaches its final value takes placein a single reduction stage. The invention also contains the possibilityof reducing the thickness of the material in a number of consecutivereduction stages, before finally reducing the thickness of the materialto approximately 1/3 of its original thickness in a final stage. In thiscase the draw ring or draw rings will consist of a number of ringsections for the consecutive gradual reduction of the thickness of thematerial. The embodiment described in this paragraph is used mainly whenthe material in the blank has a large wall thickness and/or when thedraw rings are moved at high speed.

Tubular blanks of circular cross-section have been shown in the abovedescription. The invention may, of course, also be applied to tubularblanks of other cross-sections.

The above description relates to the plastic material polyethyleneterephthalate. The values indicated in the description for thereductions in thickness and temperature are therefore also related tothis material. A large number of materials of the polyester or polyamidetype are known to exist, however, and to have similar characteristics,for which reason the invention as such is also applicable either inwhole or in part to these materials, provided that the reductions inthickness and the temperatures are adjusted to suit the specificrequirements of the respective material. The following are typicalmaterials for which the present invention is suitable, after theindicated adjustments have been made: polyethylene terephthalate,polyhexamethylene adipamide, polycaprolactam, polyhexamethylenesebacamide, polyethylene-2,6- and 1,5-naphthalate,polytetramethylene-1,2-dioxybenzoate, and copolymers of ethyleneteraphthalate, ethylene isophthalate, and other similar plasticpolymers.

The crystallinity values stated in the present application relate to thetheories disclosed in the publication "Die Makromolekulare Chemie" 176,2459-2465 (1975).

What is claimed is:
 1. A tubular object of polyethylene terephthalateformed from a tubular blank consisting of material with a crystallinityof less than 10%, said object having a cylindrical part which consistsof material which is oriented along the axis of the object only and hasa maximum crystallinity of approximately 30%, the material of saidcylindrical part being obtained by reducing the thickness of the blankwhile substantially maintaining its diameter whereby said cylindricalpart has substantially equal thickness over its length.
 2. An object asclaimed in claim 1 wherein said maximum crystallinity is between 10 and25%.
 3. An object as claimed in claim 1 wherein said maximumcrystallinity is 17%.
 4. An object as claimed in claim 1 wherein thereduction of the thickness of the blank is obtained with the blank at atemperature in the vicinity of the glass transition temperature of thematerial.
 5. An object as claimed in claim 4 wherein said temperature isno more than 30° C. greater than the glass transition temperature.
 6. Anobject as claimed in claim 1 wherein the thickness of the cylindricalpart is a multifold reduction of the thickness of the blank.
 7. Atubular object of polyethylene terephthalate formed from a blankconsisting of material with a crystallinity of less than 10%, saidobject having a cylindrical part which consists of material which isoriented along the axis of the object only and has a maximumcrystallinity of approximately 30%, the material of said cylindricalpart being obtained by forming a transitional zone between a region ofthinner, oriented material and a region of thicker material anddisplacing said transitional zone to elongate the region of thinnermaterial and reduce the region of thicker material whereby saidcylindrical part has substantially equal thickness over its length. 8.An object as claimed in claim 7 wherein said maximum crystallinity isbetween 10 and 25%.
 9. An object as claimed in claim 8 wherein saidmaximum crystallinity is 17%.
 10. An object as claimed in claim 7wherein the reduction of the thickness of the blank is obtained with theblank at a temperature in the vicinity of the glass transitiontemperature of the material.
 11. An object as claimed in claim 10wherein said temperature is no more than 30° C. greater than the glasstransition temperature.
 12. An object as claimed in claim 7 wherein thethickness of the cylindrical part is a multifold reduction of thethickness of the blank.
 13. A tubular object of polyethyleneterephthalate comprising a cylindrical part consisting of material whichis oriented along the axis of said part only and has a maximumcrystallinity of approximately 30%, the orientation and crystallinity ofthe material of said cylindrical part being obtained by applying axialforce to a tubular blank of said material in amorphous state over a partof the thickness of the blank to reduce the thickness substantially bythe amount of the part engaged while elongating said tubular blank toproduce the crystallinity and monoaxial orientation of the material ofsaid cylindrical part whereby said cylindrical part has substantiallyequal thickness over its length.
 14. An object as claimed in claim 13wherein said maximum crystallinity is between 10 and 25%.
 15. An objectas claimed in claim 14 wherein said maximum crystallinity is 17%.
 16. Anobject as claimed in claim 13 wherein the reduction of the thickness ofthe blank is obtained with the blank at a temperature in the vicinity ofthe glass transition temperature of the material.
 17. An object asclaimed in claim 16 wherein said temperature is no more than 30° greaterthan the glass transition temperature.
 18. An object as claimed in claim13 wherein the thickness of the cylindrical part is a multifoldreduction of the thickness of the blank.
 19. A tubular object as claimedin claim 1 comprising a closed end.
 20. A tubular object as claimed inclaim 7 comprising a closed end.
 21. A tubular object as claimed inclaim 13 comprising a closed end.